Variable speed motor drive



May 14, l940 n 1.. A. KlLGoRE 2,201,006

VARIABLE SPEED MOTOR DRIVE Filed Oct. 18, 1958 2 Sheets-Sheet 1 E @E K s: ,Mgt

' jg E v3 "Q5 E Q Q5 WITNESSESI INVENTOR i' f/2 Le@ Azlgore. /f BY 2. f/ffm ATTORNEY May M 1940 1 A. KILGoRE n VARIABLE SPEED MOTOR DRIVE Filed Oct. 18, 1938 2 Sheets-Sheet` 2 mw NER ..0 mml e. RW m my MK. A 6 6 L Br/f JM ATTORNEY STTES PTENT accrocs vamente sesso Moron parve Lee n. Kilgore, Forest Hills, Pa., assigner to 'Westinghouse Electric a Manufacturing Company, East Eittsburgh, Pa., a corporation of Permsylvania Application october 1s, icas, semi No. 235,533

d Claims. (im. 1mm-274) My invention relates to a variable speed motor main induction motor l but obviously the direct drive, and particularly to a control system for current motor l may be utilized either to drive a assuring constant control of a rectifier controlseparate load or to drive a suitable generator for ling the output oi" the secondary' of a wound feeding back the secondary current to the main 5 rotor induction motor. alternating current supply circuit 3.A o

It hasheretorore been proposed to construct a The full wave rectifier 6 preferably comprises variable speed motor drive` by employing a wound a plurality of make-alive type valves l il, individu rotor induction motor. as the main driving eleual valves l0 being enclosed in individual conment and to control the output oi' thelwound tainers each of which. includes a main anode li,

lll rotor by means oi a controlled rectilier; prefercathode I2 and asultable maire-alive electrode i3. l0 ably feeding the rectified current to an auxiliary Preferably the maire-alive electrodes i3 are supdirect current rnotor mechanically coupled to the plied with make-alive current by means of a suitrnain driving nriotor. Because of the comxnutaableV connection to the corresponding anodes il, tion of the rectifier device, the output voltage of the flow of current being controlled by auxiliary l5 the wound rotor secondary is very irregular somegrid controlled valves 'it herein illustrated as oi l5 times falling to substantially zero, so that if the the hot cathode type. secondary potentiel is utilized to control the rec- In order to secure a control potential having a tiier device, there is considerable danger of false frequency corresponding to the slip frequency of operation oi the control device and consequent the main motor i, l provide a pilot induction 2o loss of control in the rectifier device resulting in generator l5 similar to a wound rotor induction @o undesirable speed variations in the motor drive. motor coupled directly to the main induction It is an object or" my invention to provide such motor l. The primary lo of this pilot generator a motor drive in which. the control potential for is supplied with energy preferably from the main the converter is provided which has a suitable, alternating current source t so that the output as preferably smooth sine Wave form, so that the Y frequency of the secondary Winding is identical @s `control oi the converter will not be lost because with the output frequency or slip frequency of oi variations or irregularities in the secondary the secondary il oi the main induction rnotor i. output of 'the `wound rotor driving moton For ln. order to provide speed control for the main securing this smooth control potential prefer induction motor l, a suitable phase shifter ill lio to employ an auxiliary wound rotor pilot genherein indicated as an induction phase shifter is so erator 'directly coupled to the driving shaft of connected in series with pilot generator i5. The the main motor so that the auxiliary pilot genphase shifter 2li is preferably located between the crater hasta frequency corresponding to the slip pilot generator iii and the control transformer frequency oi the main driving motor. 22 as in this position the minimum size device @ther objects and advantages of my invention can be utilized as only the actual control energy @s will he apparent from the detailed description is handled. However, it may at times be desire token il! 'ollliictin with the accompanying able t0 shift the phase relation of the primary. in

drawings, in which: stead oi the secondary or output potential in Flglle iS @u diiglmmaic lai/'Out 0f a mOtOl which case the phase shifter 20 will be inserted 4S@ drive according to my invention, between the alternating current supply 3 and w FlgjZ is a schematic diagram of the connecthe pilot generator lli. The control grids il oiJ tions according to my invention, and the auxiliary valves ll are then supplied with Fig. 3 isa diagrammatic representation of the control potential through a suitable control secondary potential oi the Wound rotor induction transformer by the phase controlled output 45 motor. potential of the pilot generator The motor drive according to my invention ln the operation oi the motor drive according comprises e Wound rotor induction motor l having to my invention, the speed of the in induction a primary winding t connected to a suitable source motor i is controlled by shifting phase rela of alternance current Si and a Secondary windtion or" trie output potential ein@1 peut generator 50 ing fl connected by means ci suitable slip rings ii i5 so that the current drawn o the secondary 59 to a :lull wave rectifier t, preferably of the makel of the main driving motor i is controlled. The alive typen The `rectified output of the second rectified secondary current is preferably fed to a ary Winding il of the induction motor l is supsuitable direct current motor 'l so that 'the sysplied to a suitable direct current motor l, prefertem has a constant horsepower output.

Vgli; ably directly oonnectedtothe drive shaft t ofthe Because of the control 'of the rectiier 8 the M potential of the secondary 4 has a iluctuating potential as shown in Fig. 3 in which a single phase of the output potential is diagrammatlcally illustrated. When the rectifier 6 is operating with considerable angle of delay. the phase potential of the secondary 4 builds up along the normal wave form thenat the instant of firing of the valve iii of the converter B the phase potentials commutate at which 'time there is an essential short circuit between phase producing a dip in the phase voltage which, at maximum delay, may approach zero, however, as the control potential for the rectifier 6 is produced by ani-independent pilot generator the control of the valves is in no' wise affected by the fluctuations of the secondary voltage of the main motor l.

For purpose of illustration I have shown and described a specific embodiment of my invention. It will be apparent that changes and modifications can be made therein without departing from the true spirit of my invention cr the scope of the appended claims.

I claim as my invention:

1. A variable speed motor drive comprising a wound rotor induction motor having a primary and a secondary winding, means for supplying ing the potential of the secondary winding of said pilot generator for controlling the application of control potential'to said control electrodes.

2. A variable speed motor drive comprisingv a wound rotor induction motor including a primary and a secondary winding, a source of polyphase alternating current connected to the primary Winding of said induction motor, a direct current motor, feeding connections for feeding said direct current motor from said secondary winding, a vpolyphase full wave, make-alive type valve converter interposed in said feeding oonnections, a. pilot generator coupled with said wound rotor induction motor, said -pilot generator having an output frequency equal to the slip frequency of the wound rotor induction motor, make-alive electrodes for initiating current flow in said converter, make-alive connections including grid controlled auxiliary valves, means including control transformer means for impressing the pilot generator potential on the grids of said auxiliary valves for controlling the operation of said make-alive type converter.

3. A variable speed motor drive comprising a wound rotor induction motor including a primary and a secondary Winding, a source of polyphase alternating current connected to the primary winding of said induction motor, a direct current motor, feeding connections for feeding said direct current motor from said secondary winding, a

make-alive connections including grid controlled auxiliary valves, means including control transformer means for impressing the pilot generator potential on the grid of said auxiliary valves for controlling the operation of said make-alive type valves and phase shifter means interposed between said pilot generator and said control transformer means. v

4. A variable speed motor drive comprising a wound rotor induction motor, a direct current motor, connections for supplying current from said wound rotor induction motor to said current motor, a controlled multi-valve rectifier in said connections, a pilot generator coupled to said wound rotor motor, said pilot generator having a frequency corresponding to the slip frequency of the wound rotor induction motor, control electrodes associated with the valves of said multivalve rectifier. control connections for supplying control potential to said control electrodes, auxiliary grid controlled valves in said control connections and connecting means for impressing the potential of said pilot generator on the grids of said auxiliary valves for controlling the application of control potential to said control electrodes.

5. A variable speedgmotor drive comprising a wound rotor induction motor,l a direct current motor, connections for supplying current from said wound rotor induction motor to said direct current motor, a controlled multi-valve rectifier in said connections, a pilot generator coupled to said wound rotor motor, said pilot generator having a frequency corresponding to the slip frequency of the wound rotor induction motor, control electrodes associated with the valves of said multi-valve rectier, control connections for supplying control potential to said control electrodes, auxiliary grid controlled valves in said control connections and connecting means for impressing the potential of said pilot generator on the grids of said auxiliary valves for controlling the application of control potential to said control electrodes and phase shifter means connected in series with the output potential of said pilot generator.

6. A variable speed motor drive comprising a main wound rotor induction motor, a full wave rectifier for controlling the current drawn by said main induction motor, a direct current motor supplied with current from said main induction motor through said full wave rectifier, a pilot induction generator coupled to said main induction motor for providing a control potential ot the same frequency as the secondary potential of said main induction motor, control electrodes associated with said full wave rectifier and connection for impressing the potential of said pilot generator to control the operation of said control electrodes.

LEE A. KILGORE. 

